ul,li{
    padding: 0;
    margin: 0;
    list-style: none;
}
#content{
    width: 500px;
    padding: 0;
    margin: 0;
    overflow: hidden;
    font-size: 12px;
    line-height: 25px;
    border: 1px #000 solid;
}
/*父级元素相对定位*/
#content ul{
    position: relative;
}
.tipBg,.tipText{
    position: absolute;
    height: 25px;
    width: 500px;
    top: 10px;
}
.tipText{
    color: black;
   z-index: 999; /*层级，越多优先级越高*/
}
.tipBg{
    background: #21D4FD;
    opacity: 0.5;  /*背景透明度*/
}